The root and canal anatomy of the mandibular first molar is highly complicated. A mandibular first molar with a C-shaped root canal system is rare. This article describes two different cases of this system. Case 1 has a complete C-shaped fused root. The root canal is characterized by a mesial lingual root canal and a C-shaped fused root canal. Case 2 has a C-shaped fused root in the buccal region and a distal lingual root. The root canal is characterized by a type Ⅱ-Ⅰroot canal in the buccal region and a distal lingual root canal.
下颌第一恒磨牙根管系统复杂多样，其中C形根管较为少见。本文报道2种不同类型的下颌第一恒磨牙C形根管病例。病例1，一个完整C形融合牙根，根管特点为近中舌侧位置一个根管，C形态的峡部及远中位置融合为一个根管。病例2，颊侧一个C形态融合牙根和远中舌侧一个独立牙根，根管特点为颊侧C形态区域为Ⅱ-Ⅰ型根管和一个独立的远中舌侧根管。.
Keywords: C-shaped root canal system; mandibular first molar; root canal treatment.